EP 0 831 964 B1 (Leybold Vakuum GmbH) describes a selective gas sensor comprising an evacuated housing sealed by a membrane. The membrane is made of a silicon material such as quartz, quartz glass, pyrex glass, silicon oxide, silicon nitride, silicon oxynitride, or silicon carbide, arranged on a silicon disc. The silicon discs has recesses in the form of windows in which heating walls are provided on the membrane. Such a membrane is selectively permeable to light gases such as helium or hydrogen, while it is impermeable to other gases. By the passage of gases through the membrane, the pressure in the housing, which initially holds a high vacuum, is increased. The other walls of the housing, except for the membrane, are vacuum-tight.
DE 100 31 882 A1 (Leybold Vakuum GmbH) describes a sensor for helium or hydrogen using of the principle of a selectively permeable membrane. The housing of the sensor is made of glass and the selective passage is a membrane of a silicon material that is provided with a silicon disk having through holes, as well as with a heating. The housing accommodates a gas pressure sensor in the form of a Penning arrangement or a magnetron that responds to the total pressure of the gas having entered the housing. Thus, a relatively simple gas pressure sensor may be used instead of a mass spectrometer. The gas pressure sensor has at least two electrodes arranged in the housing and, in addition, a magnet provided outside the housing and generating a magnetic field penetrating the housing. The glass housing is sensitive to impacts and is fragile. The housing of borosilicate glass has approximately the same coefficient of thermal expansion as the silicon of the membrane so that both may be connected through anodic bonding or diffusion welding. Because of the high vacuum prevailing therein, the housing must not comprise any seals or adhesives that might cause gas leakages, thereby impairing the detection limit.